The present invention relates generally to electroluminescent driver circuits and in particular the present invention relates to an electroluminescent driver circuit with improved power consumption efficiency.
An electroluminescent lamp (EL-lamp) is a light source that is typically used for portable (battery operated) electronic devices. An EL-lamp is constructed similar to a capacitor in that it has a dielectric positioned between two electrodes. In an EL-lamp, one of the electrodes is transparent. Typically, a phosphor powder is used to radiate light when a strong electrical field is applied across it. The phosphor powder may be contained in the dielectric layer or it may be in a separate layer that is adjacent the dielectric layer. The EL-lamp is illuminated when an alternating current (AC) is applied across the electrodes. An integrated driver circuit (an EL driver) is typically used to convert direct current (DC) from the battery to a desired AC current. An example of a three port EL driver is described in U.S. Pat. No. 5,347,198 to Kimball which is incorporated herein by reference.
In a typical EL driver application, the EL driver will deliver a voltage to the lamp on the order of 160 to 240 volts peak to peak. The lamp frequency is typically 100 to 800 HZ. If EL-lamps are used as backlights for color displays, a white panel will be used that may require peak-to-peak voltage swings as high as 400V. In this type of application the displays tend to be relatively large. Accordingly, the load will need to store a large amount of energy at each peak to work properly.
It is desired that the EL-lamp and its associated EL driver circuit to generate the maximum amount of illumination with minimum power drain. The efficiency of a typical integrated EL driver is generally less than 35%. This efficiency is calculated as the energy delivered to the load divided by the energy drained from the battery. Accordingly, it is desired in the art to improve the efficiency of EL-drivers.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an efficient EL-driver.
The above-mentioned problems with EL-drivers and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
In one embodiment, an electroluminescent driver circuit is disclosed. The electroluminescent driver circuit comprises a load to provide illumination, an inductor, a transistor and a plurality of switches. The inductor has a first side that is coupled to a positive terminal of a power supply and a second side that is selectively coupled to the load. The transistor is coupled to selectively conduct current from the second side of the inductor to a ground terminal of the power supply in response to a digital signal. The plurality of switches are coupled to the load to selectively charge and discharge the load, wherein the switches selectively provide a discharge path for positive charge on the load to be discharged to the positive terminal of the power supply.
In another embodiment, an electroluminescent lamp (EL-lamp) driver circuit is disclosed. The electroluminescent lamp (EL-lamp) driver circuit comprises a first inductor, a first transistor, a load and four switches. The first inductor has one side coupled to a positive terminal of a power supply. The first transistor is used to provide a cyclic charging current path from the second side of the first inductor to ground. The first transistor is cycled on and off by a first digital signal. The load is used to provide an illumination source. The load is coupled to the four switches in a H-bridge configuration. A first pair of the four switches selectively couple the load to a second side of the first inductor and a second pair of the four switches selectively couple the load to the positive terminal of the power supply. The switches are selectively opened and closed to charge and discharge the load, wherein positive charge on the load is discharged to the positive terminal of the power source.
In another embodiment, an EL-lamp circuit is disclosed. The EL-lamp circuit comprises an inductor, a charging transistor, a load and a discharging transistor. The inductor has a first side coupled to a positive terminal of a power supply. The charging transistor is used to provide a cyclic current path from a second side of the charging inductor to a negative terminal of the power supply during a charging portion of a charging/discharging cycle. The charging transistor is controlled by a digital charging signal. The load is selectively coupled to a connection between the second side of the charging transistor and the charging transistor. The discharging transistor is used to provide a cyclic current path from the load to a second side of the inductor during a discharging portion of a charging/discharging cycle. The discharging transistor is controlled by a digital discharging signal, wherein charge stored on the load is discharged to the positive terminal of the power source during a discharge cycle.
In another embodiment, an EL-lamp circuit is disclosed. The EL-lamp circuit comprises a charging inductor, a charging transistor, a load, a discharging transistor and a plurality of switches. The charging inductor has a first side coupled to a positive terminal of a power supply. The charging transistor is used to provide a cyclic current path from a second side of the charging inductor to a negative terminal of the power supply. The charging transistor is controlled by a digital charging signal. The load is selectively coupled to a connection between the second side of the charging transistor and the charging transistor. The discharging inductor has a first side coupled to the positive terminal of the power supply. The discharging transistor is used to provide a cyclic current path from the load to a second side of the discharging inductor. The discharging transistor is controlled by a digital discharging signal. The plurality of switches are coupled to the load to control the charging and discharging of the load, wherein positive charge stored on the load is discharged to the positive terminal of the power source during a discharge cycle.
In another embodiment, an EL-lamp circuit is disclosed. The EL-lamp circuit comprises a first inductor, a first transistor, a second transistor, a load, a first switch, a second switch, a second inductor and a third transistor. The first inductor has a first side and a second side. The first transmitter is used to provide a cyclic current path from a positive terminal of a power supply to the first side of the first inductor. The first transistor is cycled by a first drive signal. The second transistor is used to provide a cyclic current path from the second side of the first inductor to a ground. The second transistor is cycled by a second drive signal. The load is used to provide illumination. The load has a first electrode and a second electrode. A first switch is coupled between the current path between the first transistor and the first side of the first inductor and the first electrode of the load. The second switch is coupled between the current path between the second side of the first inductor and the second transistor and the first electrode of the load. The second inductor has a first side and a second side. The second side is coupled to the positive terminal of the power supply. The third transistor is used to provide a cyclic current path between the first electrode of the load and a first side of the second inductor. The third transistor is cycled by a discharge signal, wherein the third transistor is cycled to discharge positive charge on the first electrode of the load to the positive terminal of the power supply.
In another embodiment, a method of operating an EL-lamp circuit is disclosed. The method comprises storing positive charge on a first electrode of a EL-lamp with a power supply and discharging the positive charge stored on the first electrode to a positive terminal of a power supply.
In another embodiment, a method of operating a cycle of an EL-lamp driver circuit is disclosed. The method comprises placing a select amount of positive charge on a first electrode of a load with a power supply. Discharging the positive charge on the first electrode to a positive terminal of the power supply. Placing a select amount of positive charge on a second electrode of the load with the power supply. Discharging the positive charge on the second electrode to the positive terminal of the power supply.
In another embodiment, a method of operating a cycle of an EL-lamp driver circuit is disclosed. The method comprises placing a select amount of positive charge on a first electrode of a load with a power supply. Discharging the positive charge on the first electrode to a positive terminal of the power supply. Placing a select amount of negative charge on the first electrode of the load with the power supply. Discharging the negative charge on the first electrode to a ground.